1. Field of the Invention
The present invention relates to a drive apparatus that drives movable parts.
2. Description of the Background Art
Driving speed of an ultrasonic motor having a piezoelectric element (electromechanical transducer element) may be adjusted by performing intermittent drive that repeats output and suspension of a driving signal (e.g. Japanese Patent Application Laid-Open No. 63-7174 (1988)).
However, such intermittent drive causes audible sound to be generated during intervals between the time of starting drive by outputting the driving signal and the time of suspending drive by suspending the driving signal.
A technique for solving this problem is disclosed in Japanese Patent Application Laid-Open No. 9-163765 (1997), for example. The technique aims to lower noise by controlling the voltage of the driving signal at the times of starting and suspending drive.
Unfortunately, it is required of the technique disclosed in the above JP 9-163765 to perform special voltage control on the driving signal each time the driving signal is switched to be output and suspended in a high-speed cycle, which requires a complicated configuration.